1. Field of the Invention
The subject invention is directed to gas turbine engines, and more particularly, to a valve assembly for modulating the flow of fuel to the combustor of a gas turbine engine for actively controlling the combustion process to maintain combustion stability and otherwise optimize engine performance.
2. Background of the Related Art
Combustion instability is a significant problem in the design of low-emission, high performing combustion chambers for gas turbines. Combustion instability is generally understood as high amplitude pressure oscillations that occur as a result of the turbulent nature of the combustion process and the large volumetric energy release within the combustion chamber. Combustion instability diminishes engine system performance, and the vibrations resulting from pressure oscillations can damage hardware components, including the combustion chamber itself. Moreover, when the combustion heat release becomes in phase with and reinforces acoustic pressure waves, a thermo-acoustic instability results.
In the past, passive control methods were employed to correct combustion instability, including, for example, modifying the fuel injection distribution pattern, or changing the shape or capacity of the combustion chamber. Passive controls are often costly and limit combustor performance. More recently, active control methods have been used to correct combustion instability by modifying the pressure within the system. One way this can be done is by sensing the amplitudes and frequencies of acoustic pressure waves, and then modulating fuel injection at frequencies out of phase with the instabilities.
Currently, fuel injector flow rates are controlled by changing the fuel pressure feeding a common fuel manifold, with no individual control to each of the fuel injectors. For example, U.S. Pat. No. 6,672,071 discloses a combustion control system that includes a fuel pulsator communicating with a plurality of fuel injectors through a manifold. Fuel is pulsed to the injectors through the manifold at a frequency that promotes stable combustion.
Combustion stability could be achieved more effectively with active controls, if fuel flow could be modulated or pulsed at each fuel injector individually. Furthermore, if fuel flow could be pulsed to each fuel injector at high frequencies, the droplet size of fuel could be dramatically reduced, which would improve ignition and optimize engine performance.
It would be beneficial therefore, to provide a valve assembly for an active combustion control system for gas turbine engines, that is designed to modulate or otherwise command pulsed fuel flow to individual fuel injectors at relatively high frequencies on the order of 1000 Hz or more, so as to effectively stabilize combustion and otherwise optimize engine performance.